Ride the Tsunami

[Wetfeet]

http://www.youtube.com/watch?v=OdhfV...e_gdata_player

Here is a link to Japenese Coast Guard video posted on Google news today.

Wetfeet

[chris07732]

How large did that wave seem to you, 10-15 ft. ? It was larger than I thought a tsunami would appear in the open ocean. Can't imagine how big it became when it hit the shore.

[boatman61]

It was still building as it was approaching shore.... not shallow enough for it to get top heavy and start to break... still just a very big swell..
hell... they didn't even raise any spray as they went down the other side...

[Dragon Lady]

Amazing how placid it looked in open water, it leaves no doubt where you want to be if you get caught in one.

[SaucySailoress]

Interesting (if a little dull). I noticed that when they reached the crest of the wave, they kept ploughing forward. Now, when we've been in huge seas we would bear away when reaching the crest, to avoid slamming the hull down on the other side and causing damage...

[SurferShane]

Thanks - that was a real eye opener!

[SurferShane]

Originally Posted by Saucy Sailoress

Interesting (if a little dull).

Bet it would have been a lot more exciting if you - or I for that matter - understood Japanese?

[SaucySailoress]

Originally Posted by SurferShane

Bet it would have been a lot more exciting if you - or I for that matter - understood Japanese?

Or if - for that matter - I had been on that boat!

[SurferShane]

Originally Posted by Saucy Sailoress

Or if - for that matter - I had been on that boat!

No doubt, although I am sure it would have been an even rougher ride in the freighter pictured in our newspapers that was picked up and dumped a mile downtown?

Unfortunately, it is even rougher ride for Japan and the rest of us who are sitting around hoping they can get the cooling at the nuclear power station online. What a horrid year already for disasters!

[roverhi]

That picture must have been taken in relatively shallow water. Having just sat through the Tsunami wave here in Kona, can tell you in deep water there was absolutely no indication when the Tsunami wave(s) passed under us.

Would really like to know just how shallow the water was that that ship was in. It's really critical for owners in making a decision on how to react to a Tsunami. The word on the Coast Guard weather broadcasts was get to water deeper than a 100 fathoms/600'. Not a problem here as it's deeper than that a 1/4 mile from shore. In areas with continental shelves like the East Coast, it would be nearly impossible to get to that depth unless you were given quite a few hours of warning and were able to get underway immediately. From experience, getting to sea is the best defense against a Tsunami if you can get into adequately deep water. The question is how deep water is adequate. Don't think 100 fathoms is a hard and fast mininum necessary depth as the Tsunami wave here was not a problem except in areas where the wave was funneled into a V shaped bay or the restricted waters of a harbor. The Tsunami Warning people need to come up with a prediction of wave height based on water depth and the general shape of the coastal area for all the coastal areas of the country.

Know that leaving a boat in a harbor is not a very good way to have your boat survive a Tsunami. Even though we had a relatively low height wave it sunk or damaged a whole bunch of boats, mostly on Maui and Keehi Lagoon on Oahu. In our harbor (Honokohau), one boat was sunk, one severely damaged, and many with fairly extensive cosmetic damage as they were repeatedly slammed up against the concrete walkways for the more than 12 hours that the surge lasted in the harbor.

[mikereed100]

Peter,

I imagine the answer is "the deeper the better" but here's what someone who actually knows what they are talking about says:

"When a tsunami finally reaches the shore, it may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore. Reefs, bays, entrances to rivers, undersea features and the slope of the beach all help to modify the tsunami as it approaches the shore. Tsunamis rarely become great, towering breaking waves. Sometimes the tsunami may break far offshore. Or it may form into a bore: a step-like wave with a steep breaking front. A bore can happen if the tsunami moves from deep water into a shallow bay or river. The water level on shore can rise many feet. In extreme cases, water level can rise to more than 50 feet (15 m) for tsunamis of distant origin and over 100 feet (30 m) for tsunami generated near the earthquake's epicenter. The first wave may not be the largest in the series of waves. One coastal area may see no damaging wave activity while in another area destructive waves can be large and violent. The flooding of an area can extend inland by 1000 feet (305 m) or more, covering large expanses of land with water and debris. Flooding tsunami waves tend to carry loose objects and people out to sea when they retreat. Tsunamis may reach a maximum vertical height onshore above sea level, called a run-up height, of 30 meters (98 ft). A notable exception is the landslide generated tsunami in Lituya Bay, Alaska in 1958 which produced a 525 meter (1722 ft) wave."

Physics of Tsunamis


Mike

[SaucySailoress]

Thanks for the link - that was, indeed, a very informative read.

[Chipg]

@ roverhi,

I'm sure you prob saw this on your local news but if not it's worth a view. Friends were 11 blocks from where this was shot (not by them).

http://www.youtube.com/watch?v=91Wh0...e_gdata_player

[Chipg]

Notice in he last 2 seconds how the bay looked like glass prior to 1 min 30 sec before. Amazing!

[roverhi]

Looks like that video was taken about 7am, 3 hours after the Tsunami hit the Big Island. I was motoring around Kailua Bay just offshore of where the video was taken. Had absolutely no indication of what was going on on shore. I hadn't seen the video, Mahalo for posting it.

Still no answer how deep and under what conditions it's safe to be at sea in a Tsunami. The wave that the ship rode over was way more destructive and higher when it hit shore. There is evidence of a way large Tsunami hitting the East Coast in prehistoric times. Supposedly the fault that caused that Tsunami is off of Africa so should have plenty of warning if it happened again. I'd be looking for information as to how far offshore I'd have to go if I had a boat the right coast.